Selection of cardiac capture verification modes

ABSTRACT

Systems and methods provide for selection of automatic capture verification modes. A number of capture verification modes are evaluated, wherein at least one of the capture verification modes has a distinct temporal relationship between delivery of a pacing pulse and detection of capture of heart tissue by the pacing pulse than the other capture verification modes. One or more capture verification modes are selected based on the evaluation. Capture verification is implemented using the selected one or more capture verification modes.

RELATED PATENT DOCUMENTS

This application is a divisional of U.S. patent application Ser. No.11/284,216 filed on Nov. 21, 2005, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to cardiac rhythm managementmethods and devices and, more particularly, to selection of one or morecapture verification modes.

BACKGROUND

The healthy heart produces regular, synchronized contractions. Rhythmiccontractions of the heart are normally controlled by the sinoatrial (SA)node, specialized cells located in the upper right atrium. The SA nodeis the normal pacemaker of the heart, typically initiating 60-100 heartbeats per minute. When the SA node is pacing the heart normally, theheart is said to be in normal sinus rhythm (NSR).

Bradycardia occurs when the heart rhythm is too slow. This condition maybe caused, for example, by delayed impulses from the SA node, denotedsick sinus syndrome, or by a blockage of the electrical impulse betweenthe atria and ventricles. Bradycardia produces a heart rate that is tooslow to maintain adequate circulation.

Implantable cardiac rhythm management systems, such as pacemakers, havebeen used as an effective treatment for patients with bradycardia. Thesesystems typically comprise circuitry to sense signals from the heart anda pulse generator for providing electrical pulses to the heart. Leadsextending into the patient's heart are connected to electrodes thatcontact the myocardium for sensing the heart's electrical signals andfor delivering pulses to the heart in accordance with various pacingtherapies.

Pacemakers deliver low energy electrical pulses timed to assist theheart in producing a contractile rhythm that maintains cardiac pumpingefficiency. Pace pulses may be intermittent or continuous, depending onthe needs of the patient. There exist a number of categories ofpacemaker devices, with various modes for sensing and pacing the heart.Single chamber pacemakers may pace and sense one heart chamber. Atypical single chamber pacemaker is connected to a lead extending eitherto the right atrium or the right ventricle. Dual chamber pacemakers maypace and sense two chambers of the heart. A typical dual chamberpacemaker is typically connected to two leads, one lead extending to theright atrium and one lead to the right ventricle. Biventricularpacemakers may be used to provide pacing pulses to both the leftventricle and the right ventricle. Biventricular pacing may beparticularly advantageous for delivering cardiac resynchronizationtherapy for patient's suffering from congestive heart failure (CHF).

If a pace pulse produces a contraction or “captures” the heart tissue,an electrical signal associated with the contraction may be detected andused to confirm that capture has occurred. Pace pulses that fail toproduce a contraction in the heart tissue result in non-capture.Non-capture may occur when the pacing pulse energy is too low, and/or ifthe pacing pulse is delivered during a refractory period of the cardiactissue.

The present invention involves enhanced methods and systems forverifying capture and provides various advantages over the prior art.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to methods and systemsfor implementing selection of automatic capture verification modes. Oneembodiment involves a method for automatically implementing captureverification in a cardiac rhythm management system. A number of captureverification modes are evaluated. At least one of the captureverification modes has a distinct temporal relationship between deliveryof a pacing pulse and detection of capture of heart tissue by the pacingpulse than the other capture verification modes. One or more captureverification modes are selected based on the evaluation. Captureverification is implemented using the selected one or more captureverification modes.

The at least one capture verification mode may comprise a single chambercapture verification mode or may comprise a multi-chamber captureverification mode.

According to various aspects of the invention, the at least one captureverification mode may use the same capture verification algorithm or adifferent capture verification algorithm than the other captureverification modes. The at least one capture verification mode may usethe same sensing vector or a different sensing vector than the othercapture verification modes. The at least one capture verification modemay use a sensing vector for detecting capture that is spatially moredistal from the pacing vector than a sensing vector used for detectingcapture by the other capture verification modes.

In one implementation, the plurality of capture verification modes maybe evaluated during a capture threshold test. In another implementation,the plurality of capture verification modes may be evaluated on a beatby beat basis. The evaluation of the capture verification modes mayinvolve sensing for capture using each of the plurality of captureverification modes based on cardiac signals of one cardiac cycle.Alternatively, the evaluation of the capture verification modes mayinvolve sensing for capture using each of the plurality of captureverification modes based on cardiac signals of multiple cardiac cycles.

In some implementations, the one or more capture verification modes maybe selected based at least in part on a hierarchy of captureverification modes. In other configurations, the one or more captureverification modes may be selected based at least in part on a temporalproximity of capture detection of the one or more capture verificationmodes to the timing of the pacing pulse. In further implementations, theone or more capture verification modes may be selected based at least inpart on the reliability of capture detection of the selected capturedetection mode. If multiple capture detection modes are selected,capture verification may be implemented using a combination of themultiple capture detection modes. For example, a first captureverification mode may be confirmed by a second capture verificationmode. The plurality of capture verification modes may be re-evaluatedand the selection may be modified. For example, re-evaluation may occurperiodically, or upon detection that patient conditions have changed.

Another embodiment of the invention is directed to a cardiac captureverification system. The system includes sensing circuitry configured tosense cardiac response signals to a pacing pulse associated with captureverification modes. Capture detection circuitry is configured to analyzethe cardiac response signals to detect capture in accordance with theplurality of capture verification modes. The capture verification modesinclude at least one capture verification mode of the plurality ofcapture verification modes having a distinct temporal relationshipbetween delivery of a pacing pulse and detection of capture of hearttissue by the pacing pulse than other capture verification modes of theplurality of capture verification modes. A processor is coupled to thecapture detection circuitry. The processor is configured to evaluate thecapture verification modes and to select one or more captureverification modes for implementation based on the evaluation.

According to one aspect of the invention, the sensing circuitry includesa first electrode configured to sense a first cardiac response signalused for capture detection in a first capture verification mode and asecond electrode configured to sense a second cardiac response signalused for capture detection in a second capture verification mode. Thefirst electrode is spatially more distant from a pacing electrode thanthe second electrode. In various configurations, one or more of thecardiac response signals may be sensed using a pacing electrode, adefibrillation coil, or other electrode. In various implementations, oneor more of the cardiac response signals may comprise a wireless ECGsignal, a surface ECG signal, a T-wave signal, or an electrogram signal.

The processor is may be configured to evaluate the plurality of captureverification modes using the plurality of cardiac response signalssensed during one cardiac cycle. Alternatively, the processor may beconfigured to evaluate the plurality of capture verification modes usingthe plurality of cardiac response signals sensed during a sequence ofcardiac cycles.

According to some aspects, selection of the capture verification modesmay be based at least in part on a temporal proximity of capturedetection determined by the one or more capture verification modes tothe timing of the pacing pulse.

According to another aspect, the capture verification system may includea memory configured to store a hierarchy of capture verification modes.The processor may be configured to select the one or more captureverification modes based at least in part on the stored hierarchy ofcapture verification modes.

According to a further aspect, the processor may be configured to selectthe one or more capture verification modes to facilitate backup pacing,to enhance the reliability of capture detection, to support captureverification for multi-chamber pacing, or to provide other featuresrelated to capture verification. In some implementations, the processorselects multiple capture verification modes for implementation as acombination.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method for implementing captureverification accordance with embodiments of the invention;

FIG. 2 is a diagram illustrating temporal and spatial relationships ofcapture detection and sensing electrodes used in selectablyimplementable capture verification modes in accordance with embodimentsof the invention;

FIG. 3 illustrates the temporal relationship between cardiac signalfeatures used for capture detection in various capture verificationmodes that may be selected for implementation in accordance withembodiments of the invention;

FIG. 4 is a block diagram of a system for selectively implementing oneor more capture verification modes in accordance with embodiments of theinvention;

FIG. 5 is a diagram conceptually illustrating selection of captureverification modes in accordance with embodiments of the invention;

FIGS. 6 and 7 are flowcharts illustrating single beat and multiple beatACV mode evaluation, respectively, in accordance with embodiments of theinvention;

FIG. 8 is a partial view of one embodiment of an implantable cardiacrhythm management device capable of implementing capture verificationprocesses in accordance with embodiments of the invention; and

FIG. 9 is a block diagram of cardiac rhythm management device that maybe used to implement capture verification in accordance with embodimentsof the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings that form a part hereof, and inwhich are shown by way of illustration, various embodiments by which theinvention may be practiced. It is to be understood that otherembodiments may be utilized in accordance with the invention, andstructural and functional changes may be made without departing from thescope of the present invention.

Cardiac rhythm management (CRM) devices such as pacemakers operate tostimulate the heart tissue via implanted electrodes to producecontractions of the heart tissue. Whether an applied electrical pacingstimulus from the implanted electrodes produces a contraction, or“captures” the heart tissue may be determined by evaluating post-paceelectrical signals produced by the heart. Automatic capture verification(ACV) refers to the ability of the CRM device to sense whether adelivered pacing pulse stimulates the myocardium. A CRM device mayperform ACV by evaluating sensed cardiac signals to determine if captureoccurs after a pacing pulse is delivered to the heart.

Various modes for performing ACV have been implemented to verify whenpacing stimuli result in cardiac capture. Different ACV technique mayuse different approaches in order to overcome various technologicalconstraints, allowing for a broad implementation of the ACV feature.Each ACV technique brings with it a different set of implementationrequirements, operating constraints, and functionalities, resulting indifferent ACV techniques being more appropriate than others fordifferent patients, different operating conditions, or different deviceparameters.

The ability to implement ACV temporally local to the stimulation site ispreferred for therapeutic purposes. Temporally local ACV analysis, e.g.within about 80 ms from the time the pacing pulse is delivered, providesthe ability to rapidly evaluate the capture status and to provide backuppacing, if necessary. ACV analysis that is temporally more distal fromthe time of pacing, e.g., greater than about 100 ms from the time thepacing pulse is delivered, requires a longer time window to evaluate thecapture status, relegating these approaches to a more diagnostic role.In general, the local ACV implementations are more sensitive to localelectrophysiological phenomena, such as lead polarization, virtualelectrode effects, and other phenomena, whereas the temporally distalapproaches are in general more immune to such phenomena, and thus morerobust.

Embodiments of the present invention describe a method by which multipleACV modes may be integrated to enhance the device functionality tailoredto the needs of an individual patient. The ACV modes provided by thedevice may be evaluated serially or in parallel and one or more of theavailable ACV modes are selected and implemented for captureverification. For example, the ACV modes may be evaluated based on theirability to provide reliable capture detection, fusion response, noiseimmunity, ability to support multi-chamber/multi-site pacing, ability tosupport different lead types, ability to provide ACV during and aftermode switch operations, whether or not the patient needs frequent orless frequent pacing energy adjustments, and/or other factors. Combiningmultiple ACV modes may be used to provide a hybrid ACV methodology. Ifmore than one ACV mode is selected, the more temporally distal ACV modeor modes may be used to confirm the more temporally local ACV mode ormodes which are more sensitive to local phenomena. The evaluation andselection of ACV modes allows a device to dynamically alter its ACVapproach to deliver enhanced diagnostic and therapeutic functionality tothe patient, without substantially reducing the level of patient safety.

In accordance with embodiments of the invention, capture verification isimplemented through the evaluation and selection of one or more suitableACV modes. More specifically, an implantable CRM device may executeprocesses for evaluating post-pace electrical signals produced by theheart during a capture threshold procedure and/or on a beat by beatbasis. The CRM device selects the most appropriate ACV mode the patientcan support based on the evaluation. Selection of the ACV mode may bebased on a preferred hierarchy of ACV modes. The preferred hierarchy mayinvolve a default hierarchy stored in the device memory and/or mayinvolve a hierarchy that has been input or modified by a physician orother person. In many situations, the more preferred ACV modes are modesthat provide capture detection more temporally local to the timing ofthe pacing pulse because of the increased therapeutic value of the moretemporally local modes.

The use of different ACV modes that are selectably implementable makecapture verification technology extensible to the broadest possiblepatient population. As previously discussed, each ACV mode brings withit different implementation requirements, operating constraints, andfunctionality, and different approaches may be more appropriate fordifferent patients. ACV mode selection illustrated in the embodimentsdescribed herein allows the device to evaluate multiple different ACVmodes to determine an appropriate ACV implementation for a particularpatient at a particular point in time. ACV mode selection allows the CRMsystem to compensate for technological constraints specific toparticular capture detection implementations, such as the evokedresponse sensing characteristics of pacing and defibrillationelectrodes, multi-chamber capture detection, and/or other capturedetection characteristics. ACV mode selection methodologies as describedherein may be advantageously deployed in implantable devices havingmultiple ACV modes available for operation in the same region of theheart. The ACV mode evaluation and selection methodologies described inthe exemplary embodiments allow the device to dynamically alter its ACVapproach to deliver enhanced diagnostic and/or therapeutic functionalityto the patient, without reducing the level of patient safety.

FIG. 1 illustrates a method of implementing capture verification inaccordance with embodiments of the invention. The CRM system provides120 a plurality of ACV modes that are respectively associated with aplurality of processes for detecting capture of heart tissue by a pacingpulse. The timing of capture detection for each ACV mode has a distincttemporal relationship with respect to the timing of the pacing pulse.For example, some ACV modes may rely on detection of cardiac signalfeatures occurring closer in time to the delivery of the pacing pulsethan other cardiac signal features used for other ACV modes. The ACVmodes are evaluated 130. In various embodiments, the ACV modes may beevaluated during capture threshold testing, and/or on a beat by beatbasis. One or more ACV modes are selected 140 for implementation. Theselection of ACV modes may involve identifying one or more ACV modesthat are consistent with the needs of the patient and/or the operatingparameters of the device. If more than one ACV mode is selected, theselected ACV modes may be implemented in combination or may beimplemented individually based on the presence of different patientand/or device conditions.

Following implementation, the available ACV modes may be re-evaluatedand the previous ACV mode selection may be changed to allow the deviceto adapt to changing patient and/or device conditions. For example, theACV modes may be re-evaluated periodically, e.g., nightly or accordingto some other pre-established schedule. Further, a physician maymanually request ACV mode evaluation via a remote communication sessionor during an office visit. In other implementations, an ACV modere-evaluation may be triggered following detection of an event, such asa loss of capture event, a mode switch, pacing rate change, tachytherapy delivery, thoracic impedance change, blood pressure change,weight change, and/or other event that may alter the effectiveness ofcapture verification.

According to one implementation, evaluation of the ACV modes may beperformed during a single cardiac beat, or during multiple cardiac beatsduring capture threshold testing. After performing a capture thresholdtest including ACV mode evaluation, the device may select one or moreACV modes for implementation. In another implementation, the device mayevaluate ACV modes on a beat to beat basis and dynamically switchbetween ACV modes.

As previously discussed, capture detection used for the various ACVmodes involves evaluating cardiac response signals following a deliveredpacing pulse to determine if the pacing pulse captured the heart tissue.For different ACV modes, the sensing vectors used to sense the cardiacsignals may include electrodes that have differing spatial distancesfrom the pacing electrode and/or differing temporal distances from thetiming of the pacing pulse. In general, but not always, ACV modes usingsensing electrodes located at a greater spatial distance from the pacingelectrode take a longer time to determine whether the pacing pulsecaptured the heart tissue when compared to ACV modes using sensingelectrodes that are located spatially closer to the pacing electrode. Inother words, the temporal distance of capture detection relative to thetiming of the pacing pulse may increase with the spatial distance of thesensing electrode relative to the pacing electrode. ACV modes using moredistally located sensing electrodes may take longer to detect capturedue to the delay in the arrival of the depolarization wavefront atsensing electrodes that are remote from the pacing electrode.

The signal features used for capture detection in different ACV modesmay occur at different times with respect to the timing of the pacingpulse. In general, ACV modes that rely on signal features that occur atgreater temporal distance from the timing of the pacing pulse takelonger to detect capture than ACV modes that use signal features thatoccur closer in time to the timing of the pacing pulse.

ACV modes evaluated in accordance with embodiments of the invention mayinvolve sensing cardiac signals for capture detection using intracardiacor intra-thoracic electrodes placed in, on, or near the heart or thecardiac vasculature and/or subcutaneous, non-intra-thoracic electrodesdisposed under the skin of the patient, but outside the thoracic cavity,such as electrodes disposed on the housing of an implantable device,and/or patient-external electrodes positioned on or near the surface ofthe patient's body.

In various examples, the ACV modes available for selection by a CRMdevice may include beat to beat capture detection for a single cardiacchamber, periodic single chamber automatic threshold testing, captureverification via T-wave analysis, periodic multi-chamber automaticthreshold testing, capture verification via wireless electrocardiogram(ECG) signal analysis, capture verification via analysis of a surfaceECG signal, as well as other ACV modes. The cardiac response signal maybe an externally sensed signal, such as the surface ECG, or may be animplantably sensed signal, such as a cardiac electrogram. Embodiments ofthe invention are described in terms of ACV modes as applied to theright ventricle, although the techniques described herein are notlimited to right ventricular implementations and may be applied to anyheart chamber. The ACV modes discussed herein provide an exemplary setof ACV modes that may be available for evaluation and selection inaccordance with the embodiments of the invention. Other ACV modes, oradditional ACV modes, may alternatively be evaluated and selected usingthe processes described herein.

FIG. 2 illustrates ACV modes described above as applied to captureverification for the right ventricle (RV) in accordance with oneembodiment. In FIG. 2, the X axis represents temporal distance from thestimulation time and the Y axis represents spatial distance from thestimulation site. In this implementation, the ACV modes 304-309available for evaluation and selection include beat to beat RV capturedetection 304, RV threshold testing 305, bi-ventricular thresholdtesting 306, RV capture detection via wireless ECG 307, T-wave analysisfor RV capture detection 308, and RV capture detection via surface ECG309. FIG. 2 illustrates spatial distances between sensing and pacingelectrodes and temporal distances between pacing and capture detectionfor the different ACV modes 304-309.

As illustrated in FIG. 2, the sensing vector for the beat to beat RVcapture ACV mode 304 is spatially relatively close to the pacing vectoror may include the pacing vector. For example, pacing may be deliveredon the right ventricular (RV) tip electrode to RV ring vector and thesensing vector for beat to beat capture detection may include the RV tipto Can sensing vector. The delay in sensing the depolarization wavefrontassociated with capture is relatively small, e.g., within about 70 ms,and the cardiac signal features used for capture detection occurrelatively soon after delivery of the pacing pulse.

Another ACV mode that may be selected in accordance with the processesdescribed herein is the RV threshold testing mode 305. In oneembodiment, the RV threshold testing mode 305 employs the RVdefibrillation coil for sensing the cardiac pacing response to thedelivered pacing pulse. Because the defibrillation coil is located at agreater spatial distance from the pacing electrode than the sensingelectrode used for beat to beat capture detection, there is a largersensing delay in sensing the captured response with the defibrillationcoil relative to the sensing delay for the beat to beat capture ACVmode.

Yet another ACV mode illustrated in FIG. 2 involves bi-ventricularpacing with RV or bi-ventricular capture detection 306. RV orbi-ventricular capture detection may include sensing for capture of theright ventricle or both the right and left ventricles afterbi-ventricular pacing, wherein an interventricular pacing delay (IVD)occurs between pacing the right and left ventricles. In some scenarios,for example, the interventricular pacing delay (IVD) may be up to about200 ms. The time required to evaluate the cardiac signal for capture ofthe left ventricle, right ventricle and/or both ventricles may extend toabout 100-200 ms following delivery of biventricular pacing. One exampleof the bi-ventricular ACV mode 306 involves RV or bi-ventricular capturethreshold testing implementing detection of capture for the RV or bothventricles with capture sensing in the RV only. When capture of bothventricles is detected, timing of capture detection may be affected bythe spatial distance between the sensing electrode and the pacingelectrode of the last paced ventricle, as well as by the duration of theinterventricular delay.

Another ACV mode 308 that may be used for verification of RV captureinvolves sensing the T-wave following delivery of a pacing pulse. Insome implementations, RV threshold testing may be accomplished based ondetecting a difference in the timing between delivery of the pacingpulse and the occurrence of the T-wave for captured and non-capturedbeats. Other implementations provide capture detection based on a changein the morphology of the T-wave, such as a change in the T-wave slope.

Some ACV modes illustrated in FIG. 2 involve detecting RV capture byanalyzing wireless 307 or surface 309 ECG signals. These ACV modes 307,309 use cardiac signals sensed using electrodes that are increasinglyspatially distant from the pacing electrode. Wireless ECG signals may besensed, for example, using an indifferent electrode deployed on thesubcutaneously implantable housing or header of the CRM device. SurfaceECG signals are sensed using patient-external electrodes placed on thesurface of the patient's body. These modes provide diagnosticinformation and exemplify global capture verification modes that are notgenerally used in therapy applications requiring capture detection forimplementation of back up pacing.

FIG. 3 illustrates cardiac response signals used for capture detectionin three of the ACV modes described in connection with FIG. 2: Thecardiac response signals illustrated in FIG. 3 include the cardiacresponse signal 420 used for beat to beat RV capture detection, thecardiac response signal 430 used in RV automatic threshold testing, andthe cardiac response signal 440 used for capture detection via surfaceECG, respectively. FIG. 3 illustrates the temporal distances 422, 432,442 between the cardiac signal features 421, 431, 441 used for capturedetection and the pacing pulse 411. As previously discussed, the cardiacsignal features 421 used for capture detection in the beat to beat RVcapture ACV mode have a relatively small temporal distance 422 relativeto the time 411 the pacing pulse is delivered, the cardiac signalfeatures 431 used for capture detection in RV threshold testing ACV modehave a larger temporal distance 432 relative to the time 411 of thedelivery of the pacing pulse, and the cardiac signal features 441 usedfor capture detection in the ACV mode employing a surface ECG have thelargest temporal distance 442 relative to the time of the delivery ofthe pacing pulse.

FIG. 4 is a block diagram of system for implementing captureverification in a CRM device in accordance with embodiments of theinvention. The system includes sensing circuitry 450 comprising aplurality of sense electrodes 451 used for sensing cardiac responsesignals to pacing. As previously discussed, the sense electrodes 451 mayinclude intra-cardiac, intra-thoracic, subcutaneous, and/or patientexternal electrodes. The sense electrodes 451 are coupled to the sensingchannels 454, which may include hardware, software and/or firmwarecomponents, via a multiplexer switch 452. The sense channels are coupledto the capture detection circuitry 460.

Evaluation of multiple ACV modes may be performed during a single beator during a series of beats. In one implementation, the multiplexerswitch 452 may be operable to couple various pairs of the senseelectrodes 451 to various sensing channels 454 in parallel to facilitateevaluation of multiple ACV modes during a single cardiac beat. Inanother implementation, testing a single ACV mode per beat may beaccomplished by coupling a single electrode pair 451 to a single sensechannel 454 for the duration of the beat. The electrode pair/sensechannel combination may be switched between beats to employ variouselectrode pair/sense channel combinations until all ACV modes have beentested. Alternatively, the electrode pair/sense channel combinationmaybe switched during a cardiac beat so that more than one ACV mode istested during the beat.

The capture detection circuitry 460 may include hardware, software,and/or firmware used for implementation of algorithms for detectingcapture. In this configuration, the selectable connection between thesense electrodes 451 and the sense channels 454 is controlled by the ACVmode selection circuitry 474 of the ACV mode processor 460. In additionto controlling the connections between sense electrodes 451 and sensechannels 454, the mode selection circuitry 474 may also controloperation of the capture detector 460 with respect to the circuitryand/or algorithms used for capture detection in conjunction with theparticular sense electrodes/sense channels 451, 454 employed.

The capture detector 460 is coupled to the ACV mode evaluation circuitry472 and provides information to the ACV mode evaluation circuitry and toother components of the CRM device. The capture information is used inthe evaluation of various ACV modes in accordance with embodiments ofthe invention.

Selection of one or more ACV modes based on the evaluation of the ACVmodes may be performed in view of a hierarchy of preferred ACV modesstored in memory 476 and accessible by the ACV mode selection circuitry474. For example, ACV modes that are “faster,” taking a relativelyshorter time from the time of pacing to verify capture, may be preferredover ACV modes that are “slower,” taking a relatively longer time fromthe time of pacing to verify capture. In some implementations, ACV modeselection may involve more than one ACV mode. The selected ACV modes maybe used in combination, and/or may be used at different times and/orunder different conditions. In some implementations, a relatively “fast”ACV mode may be used to make the initial capture determination. Arelatively “slow” ACV mode may be used to confirm the initial capturedetermination.

FIG. 5 is a conceptual diagram illustrating operation of the ACV modeselection process in accordance with embodiments of the invention.Initially, the system implements capture verification using a first ACVmode 520. Periodically, the system evaluates the available ACV modes andselects one or more of the ACV modes. To evaluate the available ACVmodes, the system enters an evaluation/selection mode 510, which mayinvolve performing capture threshold testing or may involve beat to beatevaluation, to evaluate one or more of the ACV modes. In one embodiment,all of the available ACV modes are tested during each paced cycle of theevaluation period. In another embodiment, the ACV modes are testedduring a series of paced cycles, with one ACV mode tested during acardiac cycle. In other embodiments, greater than one ACV mode, but lessthan all ACV modes are tested during a cardiac cycle of the evaluationperiod.

As illustrated in FIG. 5, after implementing capture verification usingthe first ACV mode 520 for a period of time, the system transitions 521to evaluation/selection mode 510. During the evaluation/selection mode510, the system tests and evaluates the available ACV modes. Followingthe evaluation, one or more of the ACV modes may be selected toimplement capture verification. In the example provided in FIG. 5, thesystem selects a second ACV mode 530 and transitions 531 to the secondACV mode 530. In some scenarios, the system may have selected atransition 522 back to the first ACV mode 520, or a transition 541 to acombination of third and fourth ACV modes 540. Capture verification isimplemented according to the second ACV mode 530 for a period of time.Periodically, the system may transition 532 into evaluation/selectionmode 510 to test the continued appropriateness of the second ACV mode530. If the second ACV mode 530 is selected again after testing, thenthe system transitions 531 back into the second ACV mode 530.Eventually, the system may transition to 522, 541 another mode or modesfor capture verification. For example, after testing, the system maydetermine that capture verification using a combination of third andfourth ACV modes 540 is most appropriate. If so, the system transitions541 to a state wherein third and fourth ACV modes 540 are used forcapture verification. The system may transition 542 from the combinationmode 540 and into 521, 531 other modes 520, 530 as appropriate.

FIGS. 6 and 7 illustrate single beat and multiple beat ACV modeevaluation, respectively, in accordance with embodiments of theinvention. Single beat and/or multiple beat ACV mode testing may occurduring the evaluation process. In single beat ACV mode testing,illustrated in FIG. 6, more than one ACV mode is tested during eachcardiac cycle of the evaluation period. In one implementation, singlebeat ACV mode testing may be performed using parallel connectionsbetween sense electrodes and sensing channels. In anotherimplementation, the different methods could be evaluated sequentially,by testing the response on a beat by beat basis.

A parallel implementation of single beat ACV mode testing is illustratedin FIG. 6. Pacing pulses 1-M are delivered 201 a, 201 b, 201 c duringthe test. After delivery of each pacing pulse 201 a, 201 b, 201 c,capture is detected using ACV modes 1-N. In the example provided in FIG.6, during each 1-M paced cycle, capture is detected using a first ACVmode 202 a, 202 b, 202 c, a second ACV mode 203 a, 203 b, 203 c, a thirdACV mode 204 a, 204 b, 204 c, and continuing to an Nth ACV mode 205 a,205 b, 205 c. For example, the system may detect capture using the sensevectors and processes used for beat to beat RV capture, using the sensevectors and processes used for RV threshold testing, using the sensevectors and processes used for bi-ventricular capture detection, usingthe sense vectors and processes used for wireless ECG, using the sensevectors and processes used for surface ECG, and using the sense vectorsand processes used for T-wave analysis. During testing, a fastest ACVmode may be performed first, with slower ACV modes performed later basedon their temporal distance from the timing of the pacing pulse.

After 1-N ACV modes have been tested during 1-M paced cardiac cycles,the ACV modes are evaluated 206 and one or more of the ACV modes areselected 207 for implementation. As previously discussed, in someembodiments, the selection may be based on a pre-established hierarchyof preferred ACV modes. The preferred hierarchy may take into accountpatient conditions, device conditions, history of success of particularACV modes, and/or other factors in making the ACV mode selection.

FIG. 7 illustrates sequential testing of ACV modes during capturethreshold testing. During sequential testing, a single ACV mode istested during a paced cardiac cycle. As illustrated in FIG. 6, ACV mode1 is tested during A paced cycles, ACV mode 2 is tested during B pacedcycles, and ACV mode N is tested during C paced cycles. Capture isdetected using the first ACV mode 221 a, 223 a, 225 a following deliveryof pacing pulses 1-1 through 1-A 220 a, 222 a, 224 a. Capture isdetected using the second ACV mode 221 b, 223 b, 225 b followingdelivery of pacing pulses 2-1 through 2-B 220 b, 222 b, 224 b. Captureis detected using the Nth ACV mode 221 c, 223 c, 225 c followingdelivery of pacing pulses N-1 through N-C 220 c, 222 c, 224 c. After ACVmodes 1-N have been tested during the paced cardiac cycles, the ACVmodes are evaluated 226 and one or more of the ACV modes are selected227 for implementation.

Referring now to FIG. 8 of the drawings, there is shown an implantableCRM system that may be used to implement the above described selectionof ACV modes according to the present invention. The CRM system in FIG.8 includes a pacemaker/defibrillator (PD) 800 electrically andphysically coupled to a lead system 802. A capture detector and ACV modeprocessor described in connection with FIG. 4, and elsewhere herein, maybe disposed within the housing of the PD 800 along with sensing, controland therapy circuitry. The housing and/or header of the PD 800 mayincorporate one or more electrodes 908, 909 used to provide electricalstimulation energy to the heart and/or to sense cardiac electricalactivity. The PD 800 may utilize all or a portion of the PD housing as acan electrode 909. The PD 800 may include an indifferent electrodepositioned, for example, on the header or the housing of the PD 800. Ifthe PD 800 includes both a can electrode 909 and an indifferentelectrode 908, the electrodes 908, 909 typically are electricallyisolated from each other.

The lead system 802 is used to detect electric cardiac signals producedby the heart 801 and to provide electrical energy to the heart 801 undercertain predetermined conditions to treat cardiac arrhythmias. The leadsystem 802 may include one or more electrodes used for pacing, sensing,and/or defibrillation. In the embodiment shown in FIG. 8, the leadsystem 802 includes an intracardiac right ventricular (RV) lead system804, an intracardiac right atrial (RA) lead system 805, an intracardiacleft ventricular (LV) lead system 806, and an extracardiac left atrial(LA) lead system 808. The lead system 802 of FIG. 8 illustrates oneembodiment that may be used in connection with the ACV mode selectionmethodologies described herein. Other leads and/or electrodes mayadditionally or alternatively be used.

The lead system 802 may include intracardiac leads 804, 805, 806implanted in a human body with portions of the intracardiac leads 804,805, 806 inserted into a heart 801. The intracardiac leads 804, 805, 806include various electrodes positionable within the heart for sensingelectrical activity of the heart and for delivering electricalstimulation energy to the heart, for example, pacing pulses and/ordefibrillation shocks to treat various arrhythmias of the heart.

As illustrated in FIG. 8, the lead system 802 may include one or moreextracardiac leads 808 having electrodes, e.g., epicardial electrodes,positioned at locations outside the heart for sensing and pacing one ormore heart chambers.

The right ventricular lead system 804 illustrated in FIG. 8 includes anSVC-coil 816, an RV-coil 814, an RV-ring electrode 811, and an RV-tipelectrode 812. The right ventricular lead system 804 extends through theright atrium 820 and into the right ventricle 819. In particular, theRV-tip electrode 812, RV-ring electrode 811, and RV-coil electrode 814are positioned at appropriate locations within the right ventricle 819for sensing and delivering electrical stimulation pulses to the heart.The SVC-coil 816 is positioned at an appropriate location within theright atrium chamber 820 of the heart 801 or a major vein leading to theright atrial chamber 820 of the heart 801.

In one configuration, the RV-tip electrode 812 referenced to the canelectrode 909 may be used to implement unipolar pacing and/or sensing inthe right ventricle 819. Bipolar pacing and/or sensing in the rightventricle may be implemented using the RV-tip 812 and RV-ring 811electrodes. In yet another configuration, the RV-ring 811 electrode mayoptionally be omitted, and bipolar pacing and/or sensing may beaccomplished using the RV-tip electrode 812 and the RV-coil 814, forexample. The right ventricular lead system 804 may be configured as anintegrated bipolar pace/shock lead. The RV-coil 814 and the SVC-coil 816are defibrillation electrodes.

The left ventricular lead 806 includes an LV distal electrode 813 and anLV proximal electrode 817 located at appropriate locations in or aboutthe left ventricle 824 for pacing and/or sensing the left ventricle 824.The left ventricular lead 806 may be guided into the right atrium 820 ofthe heart via the superior vena cava. From the right atrium 820, theleft ventricular lead 806 may be deployed into the coronary sinusostium, the opening of the coronary sinus 850. The lead 806 may beguided through the coronary sinus 850 to a coronary vein of the leftventricle 824. This vein is used as an access pathway for leads to reachthe surfaces of the left ventricle 824 which are not directly accessiblefrom the right side of the heart. Lead placement for the leftventricular lead 806 may be achieved via subclavian vein access and apreformed guiding catheter for insertion of the LV electrodes 813, 817adjacent to the left ventricle.

Unipolar pacing and/or sensing in the left ventricle may be implemented,for example, using the LV distal electrode referenced to the canelectrode 909. The LV distal electrode 813 and the LV proximal electrode817 may be used together as bipolar sense and/or pace electrodes for theleft ventricle. The left ventricular lead 806 and the right ventricularlead 804, in conjunction with the ICD 800, may be used to providecardiac resynchronization therapy such that the ventricles of the heartare paced substantially simultaneously, or in phased sequence, toprovide enhanced cardiac pumping efficiency for patients suffering fromchronic heart failure.

The right atrial lead 805 includes a RA-tip electrode 856 and an RA-ringelectrode 854 positioned at appropriate locations in the right atrium820 for sensing and pacing the right atrium 820. In one configuration,the RA-tip 856 referenced to the can electrode 909, for example, may beused to provide unipolar pacing and/or sensing in the right atrium 820.In another configuration, the RA-tip electrode 856 and the RA-ringelectrode 854 may be used to effect bipolar pacing and/or sensing.

FIG. 8 illustrates one embodiment of a left atrial lead system 808. Inthis example, the left atrial lead 808 is implemented as an extracardiaclead with LA distal 818 and LA proximal 815 electrodes positioned atappropriate locations outside the heart 801 for sensing and pacing theleft atrium 822. Unipolar pacing and/or sensing of the left atrium maybe accomplished, for example, using the LA distal electrode 818 to thecan 909 pacing vector. The LA proximal 815 and LA distal 818 electrodesmay be used together to implement bipolar pacing and/or sensing of theleft atrium 822.

Referring now to FIG. 9, there is shown an embodiment of a cardiacpacemaker/defibrillator (PD) 900 suitable for implementing a captureverification method evaluation and selection methodologies for a varietyof capture verification methods according to the present invention. FIG.9 shows a PD 900 divided into functional blocks. It is understood bythose skilled in the art that there exist many possible configurationsin which these functional blocks can be arranged. The example depictedin FIG. 9 is one possible functional arrangement. Other arrangements arealso possible. For example, more, fewer or different functional blocksmay be used to describe a cardiac defibrillator suitable forimplementing the methodologies for verifying capture using a number ofcapture verification methods in accordance with methods of the presentinvention. In addition, although the PD 900 depicted in FIG. 9contemplates the use of a programmable microprocessor-based logiccircuit, other circuit implementations may be utilized.

The PD 900 depicted in FIG. 9 includes circuitry for receiving cardiacsignals from a heart and delivering electrical stimulation energy to theheart in the form of pacing pulses or defibrillation shocks. In oneembodiment, the circuitry of the PD 900 is encased and hermeticallysealed in a housing 901 suitable for implanting in a human body. Powerto the PD 900 is supplied by an electrochemical battery 980. A connectorblock (not shown) is attached to the housing 901 of the PD 900 to allowfor the physical and electrical attachment of the lead system conductorsto the circuitry of the PD 900.

The PD 900 may be a programmable microprocessor-based system, includinga control system 920 and a memory 970. The memory 970 may storeinformation associated with ACV mode selection, including a storedhierarchy of preferred ACV modes, along with other information. Thehistorical data storage may include data obtained from long term patientmonitoring and may be used to develop a historical evaluation of thesuccess of various ACV modes. Stored data, as well as other information,may be transmitted to an external programmer unit 990 as needed ordesired.

The control system 920 and memory 970 may cooperate with othercomponents of the PD 900 to control the operations of the PD 900. Thecontrol system depicted in FIG. 9 incorporates a capture detector 460for detecting capture and an ACV mode processor 470 for evaluating avariety of ACV modes and selecting one or more of the ACV modes inaccordance with various embodiments of the present invention. Thecontrol system 920 may include additional functional componentsincluding a pacemaker control circuit 922, an arrhythmia detector 921,and a template processor for cardiac signal morphology analysis, alongwith other components for controlling the operations of the PD 900.

Telemetry circuitry 960 may be implemented to provide communicationsbetween the PD 900 and an external programmer unit 990. In oneembodiment, the telemetry circuitry 960 and the programmer unit 990communicate using a wire loop antenna and a radio frequency telemetriclink, as is known in the art, to receive and transmit signals and databetween the programmer unit 990 and the telemetry circuitry 960. In thismanner, programming commands and other information may be transferred tothe control system 920 of the PD 900 from the programmer unit 990 duringand after implant. In addition, stored cardiac data pertaining tocapture threshold, capture detection and/or cardiac responseclassification, for example, along with other data, may be transferredto the programmer unit 990 from the PD 900.

In the embodiment of the PD 900 illustrated in FIG. 9, electrodes RA-tip856, RA-ring 854, RV-tip 812, RV-ring 811, RV-coil 814, SVC-coil 816, LVdistal electrode 813, LV proximal electrode 817, LA distal electrode818, LA proximal electrode 815, indifferent electrode 908, and canelectrode 909 are coupled through a switch matrix 910 to sensingcircuits 931-937.

A right atrial sensing circuit 931 serves to detect and amplifyelectrical signals from the right atrium of the heart. Bipolar sensingin the right atrium may be implemented, for example, by sensing voltagesdeveloped between the RA-tip 856 and the RA-ring 854. Unipolar sensingmay be implemented, for example, by sensing voltages developed betweenthe RA-tip 856 and the can electrode 909. Outputs from the right atrialsensing circuit are coupled to the control system 920.

A right ventricular sensing circuit 932 serves to detect and amplifyelectrical signals from the right ventricle of the heart. The rightventricular sensing circuit 932 may include, for example, a rightventricular rate channel 933 and a right ventricular shock channel 934.Right ventricular cardiac signals sensed through use of the RV-tip 812electrode are right ventricular near-field signals. A bipolar RV signalmay be sensed as a voltage developed between the RV-tip 812 and theRV-ring 811. Alternatively, bipolar sensing in the right ventricle maybe implemented using the RV-tip electrode 812 and the RV-coil 814.Unipolar sensing in the right ventricle may be implemented, for example,by sensing voltages developed between the RV-tip 812 and the canelectrode 909.

Right ventricular cardiac signals sensed through use of the RV-coilelectrode 814 are far-field signals, also referred to as RV morphologyor RV shock channel signals. More particularly, a right ventricularshock channel signal may be detected as a voltage developed between theRV-coil 814 and the SVC-coil 816. A right ventricular shock channelsignal may also be detected as a voltage developed between the RV-coil814 and the can electrode 909. In another configuration the canelectrode 909 and the SVC-coil electrode 816 may be electrically shortedand a RV shock channel signal may be detected as the voltage developedbetween the RV-coil 814 and the can electrode 909/SVC-coil 816combination.

Outputs from the right ventricular sensing circuit 932 are coupled tothe control system 920. In one embodiment of the invention, rate channelsignals and shock channel signals may be used to develop morphologytemplates for analyzing cardiac signals. In this embodiment, ratechannel signals and shock channel signals may be transferred from theright ventricular sensing circuit 932 to the control system 920 and to atemplate processor where the morphological characteristics of a cardiacsignal are analyzed for capture detection.

Left atrial cardiac signals may be sensed through the use of one or moreleft atrial electrodes 815, 818, which may be configured as epicardialelectrodes. A left atrial sensing circuit 935 serves to detect andamplify electrical signals from the left atrium of the heart. Bipolarsensing and/or pacing in the left atrium may be implemented, forexample, using the LA distal electrode 818 and the LA proximal electrode815. Unipolar sensing and/or pacing of the left atrium may beaccomplished, for example, using the LA distal electrode 818 to canvector 909 or the LA proximal electrode 815 to can vector 909.

A left ventricular sensing circuit 936 serves to detect and amplifyelectrical signals from the left ventricle of the heart. Bipolar sensingin the left ventricle may be implemented, for example, by sensingvoltages developed between the LV distal electrode 813 and the LVproximal electrode 817. Unipolar sensing may be implemented, forexample, by sensing voltages developed between the LV distal electrode813 or the LV proximal electrode 817 to the can electrode 909.

Optionally, an LV coil electrode (not shown) may be inserted into thepatient's cardiac vasculature, e.g., the coronary sinus, adjacent theleft heart. Signals detected using combinations of the LV electrodes,813, 817, LV coil electrode (not shown), and/or can electrodes 909 maybe sensed and amplified by the left ventricular sensing circuitry 936.The output of the left ventricular sensing circuit 936 is coupled to thecontrol system 920.

The outputs of the switching matrix 910 may be operated to coupleselected combinations of electrodes 811, 812, 813, 814, 815, 816, 817,818, 856, 854 to various sensing circuits 931-936. An evoked responsesensing circuit 937 may be used to sense and amplify voltages developedusing various combinations of electrodes. An evoked response sensingcircuit 937 may be used to sense cardiac signals indicative of a cardiacresponse to pacing, e.g., capture or non-capture. Cardiac signalsindicative of the cardiac pacing response may be sensed and amplified bythe evoked response circuit 937 and may be analyzed by a capturedetector to determine cardiac pacing response.

The PD 900 may incorporate one or more metabolic sensors 945 for sensingthe activity and/or hemodynamic need of the patient. Rate-adaptivepacemakers typically utilize metabolic sensors to adapt the pacing rateto match the patient's hemodynamic need. A rate-adaptive pacing systemmay use an activity or respiration sensor to determine an appropriatepacing rate. Patient activity may be sensed, for example, using anaccelerometer disposed within the housing of the pulse generator.Transthoracic impedance, which may be measured, for example, via theintracardiac electrodes, may be used to determine respiration rate.Sensor information from the metabolic sensor is used to adjust thepacing rate to support the patient's hemodynamic need.

The ability to evaluate multiple ACV modes and to dynamically switchbetween ACV modes allows ACV implementation to react and adapt tochanging patient conditions, Furthermore, selection of ACV modes allowsACV to be implemented for a broad patient population. The ACV modeselection approaches described herein allow CRM devices to evaluatemultiple ACV modes and to select a most appropriate ACV implementationthat a patient can support, while reducing the physician time requiredto optimize therapy or diagnostics based on ACV mode.

Various modifications and additions may be made to the embodimentsdiscussed herein without departing from the scope of the presentinvention. Accordingly, the scope of the present invention should not belimited by the particular embodiments described above, but should bedefined only by the claims set forth below and equivalents thereof.

1. A cardiac capture verification system, comprising: sensing circuitryconfigured to sense cardiac response signals resulting from pacingpulses associated with a plurality of capture verification modes;capture detection circuitry coupled to the sensing circuitry andconfigured to analyze the cardiac response signals to detect capture inaccordance with the plurality of capture verification modes, at leastone capture verification mode of the plurality of capture verificationmodes having a temporal relationship between delivery of a pacing pulseand detection of capture of heart tissue by the pacing pulse that isdifferent from another capture verification mode of the plurality ofcapture verification modes; and a processor coupled to the capturedetection circuitry and configured to evaluate the plurality of captureverification modes, the processor configured to select one or morecapture verification modes based on the evaluation of the plurality ofcapture verification modes and based on a time interval duration of eachof the one or more capture verification modes, the time intervalduration measured between a given pacing pulse and a cardiac signalfeature used for capture detection for such pacing pulse, the processorconfigured to implement capture verification using the selected one ormore capture verification modes.
 2. The system of claim 1, wherein thesensing circuitry comprises: a first electrode configured to sense afirst cardiac response signal used for capture detection in a firstcapture verification mode; and a second electrode configured to sense asecond cardiac response signal used for capture detection in a secondcapture verification mode, the first electrode spatially more distantfrom a pacing electrode than the second electrode.
 3. The system ofclaim 1, wherein the sensing circuitry comprises a pacing electrode, andat least one of the cardiac response signals is sensed using the pacingelectrode.
 4. The system of claim 1, wherein the sensing circuitrycomprises a defibrillation coil, and at least one of the cardiacresponse signals is sensed using the defibrillation coil.
 5. The systemof claim 1, wherein at least one of the cardiac response signalscomprises a wireless ECG signal.
 6. The system of claim 1, wherein atleast one of the cardiac response signals comprises a surface ECGsignal.
 7. The system of claim 1, wherein at least one of the cardiacresponse signals comprises a T-wave signal.
 8. The system of claim 1,wherein the processor is configured to evaluate the plurality of captureverification modes using the plurality of cardiac response signalssensed during one cardiac cycle.
 9. The system of claim 1, wherein theprocessor is configured to evaluate the plurality of captureverification modes using the plurality of cardiac response signalssensed during a sequence of cardiac cycles.
 10. The system of claim 1,wherein the processor is configure to select the one or more captureverification modes based at least in part on a temporal proximity ofcapture detection determined by the one or more capture verificationmodes to the timing of the pacing pulse.
 11. The system of claim 1,comprising a memory configured to store a hierarchy of captureverification modes, wherein the processor is configured to select theone or more capture verification modes based at least in part on thestored hierarchy of capture verification modes.
 12. The system of claim1, wherein the processor is configured to select multiple captureverification modes for implementation as a combination of the multiplecapture verification modes.
 13. The system of claim 1, wherein theprocessor is configured to select a first capture verification mode anda second capture verification mode, and the second capture verificationmode is implemented by the processor to confirm the first captureverification mode.
 14. The system of claim 1, wherein the processor isconfigured to re-evaluate the plurality of capture verification modesresponsive to an event that may alter capture verificationeffectiveness.
 15. A system for automatically implementing captureverification in a cardiac rhythm management system, comprising: meansfor evaluating a plurality of capture verification modes used to operatethe cardiac rhythm management system to verify capture, at least onecapture verification mode of the plurality of capture verification modeshaving a temporal relationship between delivery of a pacing pulse anddetection of capture of heart tissue by the pacing pulse that isdifferent from another capture verification mode of the plurality ofcapture verification modes; means for selecting one or more captureverification modes based on the evaluation of the plurality of captureverification modes, including selecting based on a time intervalduration of each of the one or more capture verification modes, the timeinterval duration measured between a given pacing pulse and a cardiacsignal feature used for capture detection for such pacing pulse; andmeans for implementing capture verification using the selected one ormore capture verification modes.
 16. The system of claim 15, comprisingmeans for detecting capture using each of the plurality of captureverification modes based on cardiac signals sensed during one cardiaccycle.
 17. The system of claim 15, comprising means for detectingcapture using each of the plurality of capture verification modes basedon cardiac signals sensed during multiple cardiac cycles.
 18. The systemof claim 15, comprising means for selecting the one or more captureverification modes based on a hierarchy of capture verification modes.19. The system of claim 15, comprising means for selecting the one ormore capture verification modes based on a temporal proximity of capturedetection of the one or more capture verification modes to the timing ofthe pacing pulse.
 20. The system of claim 15, comprising means forre-evaluating the plurality of capture verification modes responsive toan event that may alter capture verification effectiveness.